The present invention relates to inkless fingerprinting systems used for identification purposes. More specifically, it relates to compositions, systems, and methods of generating instant, stable fingerprints on various substrates without the need of conventional inks and without the use of any chemical or mechanical post-treatment of the fingerprint or the surface on which the fingerprint was made.
As used herein the term "fingerprints" also encompasses "footprints" such as those taken of newly-born infants and placed on birth records. Also, the term "inkless" means the absence of colored pigments such as carbon black and as being distinct from printing inks as such term is now understood in this art.
The fingerprint patterns or ridge endings and ridge separations are highly individualized and are not altered with time. The comparison of fingerprint patterns has long been accepted as an absolute means of identifying individuals in a multitude of criminal and non-criminal situations.
In order for a fingerprinting identification system to be commercially acceptable it must be extremely stable and reliable, i.e., the prints must be distinct and clear and must be easily readable by the human eye and by automated fingerprint reading systems which are finding increased usage especially with a number of law enforcement agencies. Furthermore, the prints must form instantaneously, and must possess a high degree of stability toward exposure to extreme atmospheric conditions such as temperature, humidity and light. Preferably, the systems must be simple and aesthetically inoffensive.
Traditionally, fingerprints have been made with printing or writing types of ink, usually comprising finely ground carbon black particles dispersed in a liquid vehicle. The carbon black dispersion is ordinarily applied to a flat and firm surface, the excess dispersion removed, transferred to the surface of the object to be fingerprinted or identified, and subsequently transferred to the surface of the substrate where the final print is to be made. Such a procedure is cumbersome, time consuming and results in severe soiling of the hands and clothing of everyone involved in the fingerprinting process.
During the past several years inkless fingerprinting systems have been proposed such as disclosed in U.S. Pat. No. 3,831,552 involving the use of magnetizable powders. Other proposed inkless systems utilize the chelation of specific metal salts such as sodium vanadate with organic acids as described in U.S. Pat. No. 2,082,735, or various methods of reacting 8-hydroxyquinoline with metal salts, and preferably ferric chloride, as described in U.S. Pat. Nos. 3,960,632, 4,262,623, and 4,379,178. Additionally, U.S. Pat. No. 4,232,083 discloses the use of metal complexing compounds having a plurality of ligand groups with transitional metal salts of oleophilic, organic acids to form dark images which can be useful in fingerprinting systems.
The inkless fingerprinting systems known heretofore possess varying degrees of undesirable properties. Some are mechanically too complex to find commercial application and others, especially those relying upon metal-chelation reactions, are usually too slow and the image of the fingerprint does not appear instantaneously and in some cases it takes long periods of time before the print develops its full intensity. Oftentimes, these slow-forming inkless fingerprinting systems can be rendered completely inoperable if fingerprinting is attempted in substantially lower than ambient temperature as would be the case in an outdoor environment in geographic locations with extremely cold climates. In some cases, the fingerprint is treated chemically or mechanically after it is made in order to develop its desired color and color intensity.